1. Field of Invention
The present invention relates generally to electrical circuits and systems and, more particularly, to balanced amplifier circuits.
2. Discussion of Related Art
A balanced amplifier typically has one input port and one output port. For example, referring to FIG. 1, there is illustrated an example of a conventional balanced amplifier having a single radio frequency (RF) input 102 and a single RF output 104. The balanced amplifier comprises two chains of amplifiers 106a and 106b that are run in quadrature, that is, operating 90 degrees apart in phase. A quadrature coupler (or splitter) 108 on the RF input 102 phase-shifts the signal 90 degrees at the amplifier inputs, and a second quadrature coupler 110 on the output 104 reverses the phase shift so that the signals at the amplifier outputs combine in phase.
In some circumstances, it is desirable for a single balanced amplifier to support multiple applications, different power requirements, different modes of operation, different input and/or output filtering, or different antennae. Conventional solutions for using a single balanced amplifier in multiple modes, operating frequency bands, power settings or applications can require complicated and lossy input and output path switching or load line switching. This adds to the size and complexity of the circuit, which is often undesirable.